[PATCH] D154722: [AArch64] Refactor AArch64InstrInfo::isAsCheapAsAMove (NFC)

[Momchil Velikov via Phabricator via llvm-commits]

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- remove `FeatureCustomCheapAsMoveHandling`: when you have target features affecting `isAsCheapAsAMove` that can be given on command line or passed via attributes, then every sub-target effectively has custom handling

- remove special handling of `FMOVD0`/etc: `FVMOV` with an immediate zero operand is never[1] more expensive tha an `FMOV` with a register operand.

- remove special handling of `COPY` - copy is trivially as cheap as itself

- make the function default to the `MachineInstr` attribute `isAsCheapAsAMove`

- remove special handling of `ANDWrr`/etc and of `ANDWri`/etc: the fallback `MachineInstr` attribute is already non-zero.

- remove special handling of `ADDWri`/`SUBWri`/`ADDXri`/`SUBXri` - there are always[1] one cycle latency with maximum (for the micro-architecture) throughput

- check if `MOVi32Imm`/`MOVi64Imm` can be expanded into `MOVZ`/`MOVN`

[1] according to 19 software optimisation manuals


https://reviews.llvm.org/D154722

Files:
  llvm/lib/Target/AArch64/AArch64.td
  llvm/lib/Target/AArch64/AArch64InstrInfo.cpp

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